Monofilament having antimicrobial properties, use of such monofilaments as bristle material and brush or the like comprising said bristle material

ABSTRACT

A monofilament with antimicrobial properties for use as bristle consists of an extruded polymer with silver particles which are dispersed in the polymer matrix, and is characterized in that the silver particles have a particle size which is predominantly between 100 nm and 10 μm and are disposed along the cross-section of the monofilament with the particle size decreasing from the outside to the inside. The use of such monofilaments and brushes or paintbrushes having bristles of such monofilaments is also described.

Translation of PCT/EP02/09972 as filed on Sep. 6, 2002

The invention concerns a monofilament with antimicrobial properties for use as a bristle, consisting of an extruded polymer with silver particles which are dispersed in the polymer matrix. The invention moreover concerns the use of such monofilaments and also brushes or paintbrushes comprising bristles of such monofilaments.

The antimicrobial effect of ionized silver has been known for a long time. To obtain this effect, the silver must be present in a form in which it releases silver ions when corresponding agents, e.g. moisture, polar liquids or the like, are added. This includes in particular inorganic and organic silver salts but also elemental silver.

The antimicrobial effect of silver ions has been utilized for some time in connection with plastic articles which come in contact with the human body or which are used in an anti-bacterial environment. Self-sterilizing toothbrushes have been proposed at a very early time (GB 446,303) wherein the bristle bundles are inserted in a support made from an oligo-dynamically active metal such as silver. Moreover, the bristles are also either made from such a metal, are coated with such a metal, or incorporate the metal.

Since the inclusion of metal particles in a polymer is problematic and the particles substantially influence the material characteristics of the polymer, organic and inorganic compounds with antimicrobial effect have been proposed (EP 0 022 289, DE 3 812 616). Organic compounds cannot be worked into the molten polymer mass due to their temperature sensitivity but must be subsequently disposed on the finished product. In consequence thereof they are quickly removed under the influence of mechanical forces and the desired effect is lost after a short time. Organic compounds are usually not sufficiently insensitivity to light. The decomposition and degradation products which are produced often have adverse effects on the health.

Inorganic substances, mainly ionic compounds of silver and copper, have also been described (U.S. Pat. No. 4,525,410, EP 0 275 047, EP 0 116 865). This prior art also fails to consider possible toxic effects such as those known from copper ions. In their moist state, readily soluble salts produce a high initial surface concentration of the metal ions which quickly falls off in response to rinsing. The excessive ion concentration at first use remains largely ineffective or produces incompatibilities. The quick drop in ion concentration reduces the effect or useful time period. Compounds which are more difficult to dissolve have the adverse effect that the concentration of dissolved ions provided is too low. Continuous delivery of silver ions is supposed to produce silver zeolites (EP 0 116 865). The mass and volume fraction of the sole effective portion of the silver zeolites, i.e. the silver ions themselves, is considerably reduced due to the very large fraction of opposing zeolite ions. The inorganic load of such opposing ions considerably limits the maximum possible silver ion concentration in the polymer matrix, since the material characteristics of the polymer should remain unimpaired by the addition of the zeolite.

For these reasons, silver in its elemental form is preferred, since it can be transferred into 100% active silver ions under appropriate environmental conditions. U.S. Pat. No. 4,411,041 and GB 2 088 710 have proposed covering the heads of toothbrushes with a silver layer. However, this method is expensive and its possible applications are strongly limited. The direct inclusion of silver particles in the matrix of the polymer promises better results. DE 195 08 539 has proposed inclusion of a homogeneous distribution of mineral fillers having different grain sizes in bristle filaments of thermoplastic synthetic material, wherein the larger particles contain silver which is discharged, in a moist atmosphere, through the surface of the bristle filament in the form of ions. The larger, silver-containing particles should have a grain size of between 1 μm and 50 μm, preferably between 1 μm and 5 μm. EP 1 066 825 describes toothbrushes and other hygiene products with which the polymer matrix of the bristle filaments contains homogeneously distributed silver nanoparticles having a particle size of between 1 and 50 nm, preferably between 5 to 8 nm which should be present in a concentration of between 1 and 2000 ppm, preferably between 10 and 250 ppm. The teachings of these two documents are mutually contradictory, since DE 195 08 539 describes relatively coarse particles having a narrow grain spectrum of between 1 and 5 μm and EP 1 066 925 proposes particles in the sub micrometer range having a very narrow grain spectrum of between 5 and 8 nm.

The assignee of the instant invention has determined (DE 100 10 572) that the antimicrobial effect depends strongly on the diffusion speed of the silver ions in the polymer matrix. The assignee therefore proposed control of the diffusion speed of the silver ions from the homogeneously embedded silver particles by constructing the bristle monofilament from two polymers, one of which forms a diffusion stop for the silver ions to permit metered discharge of the silver ions with corresponding long-term effect. Even though dental tests have produced convincing results, the production method is relatively demanding.

Departing from the prior art according to EP 1 066 825, it is the purpose of the present invention to propose a monofilament with antimicrobial effects which guarantees continuous and uniform discharge of silver ions from the polymer matrix having embedded silver particles, with associated long-term effectiveness.

This object is achieved in accordance with the invention in that the silver particles have a particle size of predominantly between 100 nm and 10 μm, and are disposed such that the particle size decreases through the cross-section of the monofilament, from the outside to the inside.

The kinetics of heterogeneous non-equilibrium reactions for formation and release of silver ions from elementary silver particles depend essentially on the particle surface. For particles of ideal spherical shape, the surface area is proportional to R², wherein R is the radius of the particle. The volume and therefore the mass of such a particle are proportional to R³. The surface/mass ratio is therefore larger the smaller the particle. With the inventive combination of small particles which can be quickly activated and larger particles which are activated less quickly and which contribute to long-term maintenance of silver ion release, uniform ion discharge over a long period and therefore a long-term antimicrobial effect, is achieved.

The use of only small particles in the sub micrometer range and moreover having a narrow grain spectrum as proposed in prior art, results in rapid formation of silver ions from the particles close to the surface when moisture is added to the monofilament. However, ion formation decreases rapidly. Moreover, particles close to the surface are quickly flushed out through erosion during wear of the monofilaments. This is particularly true for particles which are directly on the surface since, when the embedded depth corresponds to the diameter, only half of the diameter of the particles is surrounded by the polymer. The smaller the particle, the faster it is released from the surface, thereby defeating its very purpose. Disadvantageously, particles in the sub micrometer range also negatively influence the crystallinity of polymers thereby reducing the impact strength.

The invention avoids use of particles in the lowermost nanometer range only, thereby preventing negative influences on the crystallinity of the polymer. In addition, a particle spectrum of 100 nm to 10 μm is selected such that formation of silver ions in response to the addition of moisture to the monofilament is effected at different speeds thereby making it uniform over a longer period of time. This is further enhanced in that the particle distribution through the cross-section of the monofilament is selected such that the particle size is reduced from the periphery of the monofilament towards the inside. With the addition of moisture, the larger particles which are close to the surface initially release less silver ions per unit surface area due to their smaller surface to volume ratio until, in response to further penetration of the moisture into the monofilament cross-section, the smaller particles which are further inside are activated and release more ions to guarantee a uniform ion release proximate the surface of the monofilament over a longer period of time. This is also advantageous since particles close to the surface are flushed out less quickly due to their larger diameter and resulting larger embedded depth and i.e. do not prematurely weaken the monofilament cross-section while maintaining their effectiveness for a longer period of time. The less active larger particles are activated with more intensity - because they are disposed close to the surface—and the released silver ions have a shorter distance to the surface, while the smaller intrinsically more active silver particles do not initially produce ions since they are disposed more deeply in the monofilament. This delay is supported by the fact that the moisture required for ion formation diffuses only slowly into the core of the monofilament and only then triggers the more active silver particles.

Practical tests have shown that the technological properties of the polymer are the least impaired, and constant ion discharge with long-term effect can be guaranteed most safely, when the majority of the silver particles have a particle size of between 250 nm and 600 nm, preferably in particular, when 80% of the silver particles have a particle size of between 150 nm and 700 nm.

The concentration of the silver in the polymer matrix should be between 10 ppm and 100,000 ppm, preferably between 500 ppm and 10,000 ppm. Practical tests of toothbrushes with bristles of monofilaments in accordance with the inventive construction which were tested under normal tooth care conditions, have shown that the antimicrobial effect does not decrease compared to the initial state even after elapse of the useful period of time for toothbrushes of 3 months, as is recommended by dentists.

The inventive monofilament can be made from polymers which are suitable for the respective purpose, e.g. a polyamide, polyester, polyolefine or also a thermoplastic elastomer.

Monofilaments with the inventive construction are preferably used as bristle material for brushes or paintbrushes. Depending on the diameter of the monofilament, an individual monofilament or a multifilament can also be used as an interdental cleaning element.

The inventive monofilament is particularly advantageous for brushes or paintbrushes in body or hair care, preferably for toothbrushes. The inventive monofilament can be advantageously used as bristle material for brushes or paintbrushes in food treatment and processing applications having increased hygienic requirements.

In particular, for applications in which the bristles or bristle bundles are very close, moisture is retained between the bristles and in the region of their mounting for a longer period of time and microorganism growth is promoted. This is counteracted by the moisture induced, simultaneous formation of ions from the silver particles of the bristles. This is particularly valid for brushes whose bristles are mechanically mounted with metal anchors in holes of a bristle support, since more ions are produced when and where moisture, which promotes microorganism growth, is present.

The invention moreover concerns a bristle or a paintbrush with a bristle support and bristles of monofilaments connected thereto in accordance with the invention, wherein the bristle support consists of a polymer with silver particles disposed in the polymer matrix, wherein the silver particles are disposed at least in the region of the bristle support which is close to the bristles.

Additional doping of the bristle support with silver particles which release silver ions when the surroundings are moist, produces an overall higher silver concentration in the region close to the bristles, in particular in the region where they are connected to the bristle support such that mainly the moisture-retaining regions of a bristle or of a paintbrush are exposed to increased silver ion concentration and microbial infection is counteracted.

The size distribution and concentration of the silver particles in the bristle support is advantageously adjusted to that of the silver particles in the bristles in dependence on the respective surrounding conditions at the location of use. For bristles or paintbrushes which come into only sporadical contact with water or aqueous liquids, the concentration of the silver particles in the bristle support is kept smaller than the concentration in the bristles. A concentration of the silver particles in the bristle support of toothbrushes of approximately 20% of the concentration of the silver particles in the bristles has shown to be sufficient.

EXAMPLE

To produce polyamide bristles for toothbrushes, a silver batch containing elementary powdery silver is added to the polyamide before extrusion. The majority of the powder particles have a size in the region of 550 nm. The silver batch is added to the polymer with a concentration of 4000 ppm. During melting, the silver particles are dispersed and distributed relatively uniformly in the molten polymer mass which is subsequently extruded into monofilaments. When suitable parameters are kept during the extrusion, the larger particles accumulate in the region close to the surface and the smaller particles accumulate in the core region of the monofilament. The filaments produced in this fashion are used as bristle material for a toothbrush and are conventionally connected to a toothbrush body. This toothbrush has then been tested under conditions similar to practice. 20 ml of a mixture of toothpaste and water has been put onto the toothbrush. Brushing for 5 minutes shows a silver ion concentration in the region of 10 μg/l. Application of a toothbrush three times a day for 3 minutes each, as is recommended by dentists, produces a total discharged amount of less than 0.5 μg.

The entire amount released is therefore also below the values defined by the European drinking water regulations, according to which drinking water must not contain more than 10 mg/l of silver ions. For specially treated water, the limit is 100 mg/l. The maximum daily intake dose of silver ions according to this regulation is 5 mg/kg of body weight. To guarantee a corresponding safety margin away from this limit, in particular also in case of continuous contact with sensitive surfaces such as the mucous membrane of the mouth, the concentration of silver ions produced during use of a toothbrush should be between 0.1 mg/l and 100 mg/l. This is guaranteed in the inventive embodiment of monofilaments as bristle material for toothbrushes. 

1-17. (cancelled).
 18. A monofilament with antimicrobial properties for use as a bristle, the monofilament comprising: an extruded polymer; and silver particles which are dispersed in a polymer matrix of said extruded polymer, wherein said silver particles have a particle size of substantially between 100 nm and 10 μm and are disposed through a cross-section of the monofilament such that a particle size decreases from an outside to an inside of the monofilament.
 19. The monofilament of claim 18, wherein a major part of said silver particles has a particle size of between 250 nm and 600 nm.
 20. The monofilament of claim 18, wherein approximately 80% of said silver particles have a particle size of between 150 nm and 700 nm.
 21. The monofilament of claim 18, wherein a concentration of silver in said polymer matrix is between 10 ppm and 10,0000 pm.
 22. The monofilament of claim 21, wherein said concentration of silver in said polymer matrix is between 500 ppm and 10,000 ppm.
 23. The monofilament of claim 18, wherein said polymer is one of a polyamide, a polyester, a polyolefine and a thermoplastic elastomer.
 24. A use of the monofilaments of claim 18 as bristle material for brushes.
 25. A use of the monofilaments of claim 18 as bristle material for paintbrushes.
 26. A use of the monofilaments of claim 18 as an interdental cleaning element.
 27. A use of the monofilament of claim 18, for body and hair care brushes or paintbrushes.
 28. The use of claim 24 for toothbrushes.
 29. A use of the monofilament of claim 18, for food treatment or processing brushes or paintbrushes.
 30. A brush or paintbrush comprising a bristle support and bristles connected therewith which are made from the monofilament of claim 18, wherein said bristle support comprises a polymer with silver particles disposed in a polymer matrix.
 31. The brush or paintbrush of claim 29, wherein said silver particles are disposed at least in a region of said bristle support which is close to said bristles.
 32. The brush or paintbrush of claim 29, wherein a size distribution and concentration of silver particles in said bristle support is adjusted to a concentration of said silver particles in said bristles.
 33. The brush or paintbrush of claim 32, wherein said concentration of silver particles in said bristle support is smaller than said concentration in said bristles.
 34. The brush or paintbrush of claim 33, wherein said concentration silver particles in said bristle support is approximately 20% of said concentration of silver particles in said bristles. 